An engineering analysis of the effect of surface tension on surface and lung recoil has been completed. The analysis suggests that tissue deformation as well as surface tension and tissue properties all contributed to the recoil pressure of the air-filled lung. Further studies have measured with micropipets the pressure around arteries and veins in excised lungs. Techniques of quantifying regional lung deformations in dogs by use of radiopaque markers have shown not only vertical gradients in lung volumes in supine dogs but also gradients in the horizontal planes. The effect of varying inspiratory flow rate on regional distribution of gas (xenon washout technique) has indicated that varying inspiratory flow rates appear to have little effect on the regional distribution of inspired gas. Also, preliminary studies using subanesthetic doses of halothane and enflurane were undertaken. Effects on the mechanical properties of the lung were rather minimal. Use of high frequency oscillation was evaluated in six dogs over a 48-hour period. Ventilation was well maintained by this technique. Small accumulations of pleural fluid were noted following the long-term HFO. This finding needs further investigation. Two factors were isolated from extracts of cotton dust. One factor was of low molecular weight and caused marked contractions of excised canine airways. Another factor of higher molecular weight caused release of serotonin from platelets. A computational model of maximal expiratory flow has been developed and the predictions of the model compare favorably with measurements from excised human lungs obtained at autopsy. The model allows manipulation of the important parameters that determine maximal expiratory flow.